Circuit-switched video-conferencing systems over ISDN connections, which are based on the H.320 standard, became available in the early 1990's. Since then, large corporations have invested large sums of money in such video-conferencing systems and the infrastructure to support them. Executives at those companies recognized the value of meeting face-to-face with key customers, suppliers, and employees. They also recognized other benefits such as reduced travel costs, shortened decision-making cycles, and increased productivity that the costly video-conferencing systems can provide.
ISDN created great opportunities for widespread adoption of video-conferencing. But, despite the benefits of ISDN, circuit-switched video-conferencing based on the H.320 standards has seen limited deployment. Many smaller companies could not justify the expense of these costly systems and the network infrastructure needed to support them.
Advances in computer and internet technologies and video compression technologies have made it possible to integrate audio and video into the personal computing environment in which video-conferencing can be delivered on computer desktops over the same packet-based networks as more traditional LAN applications such as e-mail and file transfer. With the advent of the H.323 standard for conferencing over packet-switched networks, a new type of multipoint conferencing systems has evolved. These types of multipoint bridging units (often called Multipoint Control Units or MCUs) are cheaper than ISDN-based multipoint bridging units. Often, these packet-switched multipoint bridging units contain functionality designed to enable widespread use of multimedia communication (data, audio & video) within the enterprise. One of the most notable improvements has been the development of web-based interfaces to these devices. Today, most multipoint bridges can be configured, managed and diagnosed through a simple browser-based Graphic User Interface. Furthermore, many bridges now have added capabilities to control individual conferences, call out to multi-media endpoints, disconnect endpoints, and put the conference in lecture mode.
Many multipoint bridging units are DSP-based hardware systems, which can handle computationally intensive processes such as transcoding between different audio and video compression algorithms, rate matching, and laying out one or more continuous presence views where significant video image manipulation is required. These types of DSP-based devices meet the need for video-bridging service companies, but may be too powerful and too expensive for organizations that do not require such capabilities.
Several multipoint bridging system providers, such as First Virtual Communications of Redwood Shores, Calif., the assignee of the present invention, have developed highly sophisticated software-based conferencing servers that run on off-the-shelf personal computer platforms. The performance of these software-based conferencing servers is comparable to that of DSP-based multipoint bridging units. With the performance of existing general multi-processor systems, even the more compute intensive DSP functions can be performed in software. Because they can run on low cost personal computer platforms, the software-based solutions are significantly more cost effective. In addition to providing videoconferencing capability, First Virtual Communications' conference servers provide access to a variety of integrated rich media conferencing tools, such as instant messaging and desktop collaboration.
Because conference server software is usually licensed based on the total number of simultaneous ports utilized, enterprises can install copies of the software on multiple computers without incurring significant additional costs. The computers on which the conference software is installed can be located in remote locations and close to where clusters of endpoints are located. First Virtual Communications' conference server software utilizes a technology called Intelligent Linking in this distributed conference server environment. With Intelligent Linking, the video image from each call participant (e.g., endpoint) is sent to the local conference server. By communicating with other conference servers, each conference server is aware of which video streams are being viewed by the participants connected to that server. If no one across the network happens to be viewing a particular participant's video image, the stream is not provided to the network, thus conserving network bandwidth. Audio from local endpoints are mixed at each server and the composite audio stream is sent between each server, thus conserving bandwidth and improving CPU efficiency by minimizing the audio streams processed by each MCU.
Intelligent Linking is distinct from simple cascading, which consists of starting multipoint conferences on two or more video bridges, then connecting the conferences together by having the video bridges call one another. In simple cascading, each bridge is viewed by the other bridge(s) in the call as if it were a single endpoint. With simple cascading there is no control communication between the MCUs, each MCU will decide what audio and video is send and viewable by users on the other MCUs. The problem with simple cascading is that where there are multiple callers connected to each bridge, the remote bridge users can not select which video or audio to receive from other bridges and when traditional video mixing at the MCU (Continuous Presence). The mixed multiple images from one MCU are transmitted as one video image, which appears as miniature images within a single pane on the other MCU continuous presence. Intelligent Linking can avoid these issues. By detecting what the user (endpoint) wants, Intelligent Linking can avoid the miniature tiled panes because each server is aware of the video images to be displayed. Rather than sending pre-mixed images to other conferencing servers, Intelligent Linking allows each conference server to send and receive multiple separate video and audio streams for each endpoint and mix them locally on each conference server. For instance, each endpoint may see QCIF sized images stitched together to form a single CIF sized image instead of the mini-panes from conventional bridges. With more sophisticated endpoints, like First Virtual's Conference Client, individual video streams can be sent from each MCU to allow for any number of video images to be displayed from any MCU at the endpoint. Also, with simple cascading, audio and video are always transmitted between the MCUs, so there is no conservation of bandwidth.
In earlier generations of First Virtual Communications' distributed conference server environment, each endpoint must have a pre-assigned conference server which acts as its local server. Increasingly, conferencing endpoints are installed on mobile computers which may be used in locations “far away” from its pre-assigned conference server in terms of physical distance or in terms of the number of network hops. When an endpoint is served by a conference server across the network, effectiveness of Intelligent Linking can be significantly compromised.
In view of the foregoing, there exists a need for a distributed conference server environment where Intelligent Linking can be fully utilized regardless of whether the conference endpoints are located.